Field of the Invention
This invention relates generally to touch sensors. Specifically, the invention pertains to a system and method for enabling an entire touchpad surface to mechanically move if sufficient force is used to press on the touchpad to perform a mouse click function, such as a right click or a left click.
Description of Related Art
There are several designs for capacitance sensitive touch sensors which may take advantage of a system and method for providing mechanical movement of a touchpad that is buttonless. It is useful to examine the underlying technology of the touch sensors to better understand how any capacitance sensitive touchpad can take advantage of the present invention.
The CIRQUE® Corporation touchpad is a mutual capacitance-sensing device and an example is illustrated as a block diagram in FIG. 1. In this touchpad 10, a grid of X (12) and Y (14) electrodes and a sense electrode 16 is used to define the touch-sensitive area 18 of the touchpad. Typically, the touchpad 10 is a rectangular grid of approximately 16 by 12 electrodes, or 8 by 6 electrodes when there are space constraints. Interlaced with these X (12) and Y (14) (or row and column) electrodes is a single sense electrode 16. All position measurements are made through the sense electrode 16.
The CIRQUE® Corporation touchpad 10 measures an imbalance in electrical charge on the sense line 16. When no pointing object is on or in proximity to the touchpad 10, the touchpad circuitry 20 is in a balanced state, and there is no charge imbalance on the sense line 16. When a pointing object creates imbalance because of capacitive coupling when the object approaches or touches a touch surface (the sensing area 18 of the touchpad 10), a change in capacitance occurs on the electrodes 12, 14. What is measured is the change in capacitance, but not the absolute capacitance value on the electrodes 12, 14. The touchpad 10 determines the change in capacitance by measuring the amount of charge that must be injected onto the sense line 16 to reestablish or regain balance of charge on the sense line.
The system above is utilized to determine the position of a finger on or in proximity to a touchpad 10 as follows. This example describes row electrodes 12, and is repeated in the same manner for the column electrodes 14. The values obtained from the row and column electrode measurements determine an intersection which is the centroid of the pointing object on or in proximity to the touchpad 10.
In the first step, a first set of row electrodes 12 are driven with a first signal from P, N generator 22, and a different but adjacent second set of row electrodes are driven with a second signal from the P, N generator. The touchpad circuitry 20 obtains a value from the sense line 16 using a mutual capacitance measuring device 26 that indicates which row electrode is closest to the pointing object. However, the touchpad circuitry 20 under the control of some microcontroller 28 cannot yet determine on which side of the row electrode the pointing object is located, nor can the touchpad circuitry 20 determine just how far the pointing object is located away from the electrode. Thus, the system shifts by one electrode the group of electrodes 12 to be driven. In other words, the electrode on one side of the group is added, while the electrode on the opposite side of the group is no longer driven. The new group is then driven by the P, N generator 22 and a second measurement of the sense line 16 is taken.
From these two measurements, it is possible to determine on which side of the row electrode the pointing object is located, and how far away. Using an equation that compares the magnitude of the two signals measured then performs pointing object position determination.
The sensitivity or resolution of the CIRQUE® Corporation touchpad is much higher than the 16 by 12 grid of row and column electrodes implies. The resolution is typically on the order of 960 counts per inch, or greater. The exact resolution is determined by the sensitivity of the components, the spacing between the electrodes 12, 14 on the same rows and columns, and other factors that are not material to the present invention. The process above is repeated for the Y or column electrodes 14 using a P, N generator 24
Although the CIRQUE® touchpad described above uses a grid of X and Y electrodes 12, 14 and a separate and single sense electrode 16, the sense electrode can actually be the X or Y electrodes 12, 14 by using multiplexing.
It should be understood that use of the term “touch sensor” throughout this document may be used interchangeably with “forcepad”, “buttonless touchpad”, “proximity sensor”, “touch and proximity sensor”, “touch panel”, “touchpad” and “touch screen”.
Buttonless touchpads and forcepads may be touch sensors that may not provide a user friendly haptic sensation of a mechanical “click” when pressed. While the touch sensors are still able to provide the functionality of the mouse click, they nevertheless may fail to provide tactile feedback that may not be necessary, but which may be desirable to users.
Furthermore, many touch sensors do not allow the user to perform a mechanical click, right or left, at a top portion of the touchpad. This is an inherent design issue due to the mechanical button(s) being mounted at the bottom area of the underside of the touch sensor surface because the touch sensor is hinged near the upper area of the touchpad. It may be that these types of designs allow about 80% of the touch sensor to be used for “clicking” because a mechanical click on the upper 20% of the pad is either not possible or requires excessive force.
There may be some touch sensors that do not allow any mechanical movement, but instead create an “artificial” click-type response using a motor when the user presses anywhere on the touch sensor, such as in a forcepad. There may also be other forcepad designs that create an audible “click” sound as the user presses on a touch sensor which senses mechanical pressure. However, these touch sensor also lack mechanical movement of the touch sensor itself.